The State Duma lower house of parliament approved the treaty by a vote of 334 to 73, with two abstentions, paving the way for endorsement by the upper chamber and signature by President Vladimir Putin, who has already signaled his support for the protocol.

Since the United States withdrew from the treaty, Russia held the key to whether the landmark 1997 draft agreement would cross the threshold to becoming a working international accord. For environmental groups, the ratification by Moscow marks a significant step on the road to reducing greenhouse gases.

"We will look back on today as the moment in history when humanity faced up to its responsibility," Greenpeace said in a statement Friday.

"We'll toast the Duma with vodka tonight, but on Monday morning we need to roll up our sleeves and get down to the real work," said the environmental group's climate policy advisor, Steve Sawyer.

Positive turnaround

Friday's vote resuscitated the pact that until recently was considered all but dead after President George W. Bush announced in 2001 that the United States, the world's largest polluter, wanted no further part in it. Russia, which accounts for 17 percent of the world's carbon dioxide emissions, had gone back and forth on endorsing the treaty ever since it was first drafted. But finally a month ago, Moscow government officials and Putin recommended approval.

Russia's ratification was necessary for Kyoto to go into force because the treaty stipulated that not only a majority of countries approve it, but that the signatory nations constitute 55 percent of the world's emissions.

In their discussions ahead of the vote, Russian officials hailed the financial opportunities the pact offered Moscow -- a turnaround from last year, when government leaders, including Putin had derided the protocol as too costly.

"This protocol gives Russia financial possibilities," said Valery Zubov, a deputy with the main pro-Kremlin United Russia party in the discussion before Friday's vote. "We have a chance to have a cleaner future."

Financial benefits

Russia hopes to make a short-term profit through the treaty by being able to sell off some of its quotas for greenhouse gas emissions to other industrialized signatories. The idea is that under the treaty, countries who have not exhausted their limit for emissions will be able to sell off credit -- essentially the right to pollute -- to countries needing to increase their emissions quotas. Under the pressure of the market and with an eye for profit, nations will be inclined to produce fewer emissions in order to sell more.

Point Carbon, a Norway-based consulting firm, has estimated that Russia could earn $10 billion (€8 billion) with the treaty's help by 2012.

Russian Deputy Prime Minister Zhukov said Russia would likely approach its Kyoto quotas by 2010 if the nation's gross domestic product (GDP) grew by 9 to 10 percent a year.

Pressure to ratify

Others have said Russia was pressured by the international community into ratifying the pact.

"Rusia was under unprecedented pressure," said Natalya Narochinitskaya of the nationalist Rodina (Motherland) Party. "It's ratification was presented as a stamp of a civilized country" and not based on scientific data, she said ahead of the vote.

It is widely believed that Russia agreed to sign the protocol in return for the European Union -- one of the treaty's major backers -- supporting Moscow's bid to enter the World Trade Organization.

"It's a very happy day for Europe and for me," said Margot Wallström, the Swedish EU Environment Commissioner after the Duma vote. "It sends a very forceful signal to the rest of the world."

"It is also very much a victory for the European Union," she said, in reference to the tug-of-war between Brussels and Washington over the pact.

Despite being isolated in its opposition to the protocol, the United States has refused to endorse the treaty.

"The United States' position on the Kyoto Protocol has not changed," State Department spokesman Richard Boucher said.